Anodes? aluminium boat

[golf]

have aluminium hull boat kept mostly in marina ( freshh Water ) only occasionaly trips in salt water . What anode should I use ? Zinc or Aluminium .

 

[raven]

I'm certainly no expert but would think that you need zinc anodes as zinc is a baser metal than alu (and all the metal bits on the alu boat.)

My understanding is that electrolysis corrodes the baser metal first so sacrifice the zinc and save the alu.

I'm sure someone will be along to shoot that notion out of the water if it's incorrect.

 

[VicS]

Magnesium anodes are normally used in fresh water. They may not be recommended for aluminium hulls though. They will waste away very quickly in salt water.

Zinc or aluminium anodes are used in salt water (not sure but i think zinc may be preferred for aluminium hulls but if so i dont know the reason off hand)

Zinc and aluminium anodes become coated with oxide (or basic carbonate deposit ?? ) in fresh water which renders them ineffective.

Take a look at the MG Duff website

http://www.mgduff.co.uk/leisure-craft/cathodic-protection.html
and
http://www.mgduff.co.uk/leisure-craft/hull-anode-selection/

I note however that for aluminium hulls in fresh water they suggest you contact them for advice. I think that would be wise rather that relying on opinions expressed here (including mine)

 

[tiler]

The basics of galvanic corrosion are that an electrical current is set up between dissimilar metals. The nobler will become the cathode and the less noble will become the anode. Exactly the same as a battery and the process that is used in plating with Zinc, chrome etc. Therefore, in the simplest terms whatever your hull/underwater metallic equipment is made from you need something that is less noble to protect it.

Anodic (less noble)
1. Magnesium
2. Mg alloy AZ-31B
3. Mg alloy HK-31A
4. Zinc (hot-dip, die cast, or plated)
5. Beryllium (hot pressed)
6. Al 7072 clad on 7075
7. Al 2014-T3
8. Al 1160-H14
9. Al 7079-T6
10. Cadmium (plated)
11. Uranium
12. Al 218 (die cast)
13. Al 5052-0
14. Al 5052-H12
15. Al 5456-0, H353
16. Al 5052-H32
17. Al 1100-0
18. Al 3003-H25
19. Al 6061-T6
20. Al A360 (die cast)
21. Al 7075-T6
22. Al 6061-0
23. Indium
24. Al 2014-0
25. Al 2024-T4
26. Al 5052-H16
27. Tin (plated)
28. Stainless steel 430 (active)
29. Lead
30. Steel 1010
31. Iron (cast)
32. Stainless steel 410 (active)
33. Copper (plated, cast, or wrought)
34. Nickel (plated)
35. Chromium (Plated)
36. Tantalum
37. AM350 (active)
38. Stainless steel 310 (active)
39. Stainless steel 301 (active)
40. Stainless steel 304 (active)
41. Stainless steel 430 (active)
42. Stainless steel 410 (active)
43. Stainless steel 17-7PH (active)
44. Tungsten
45. Niobium (columbium) 1% Zr
46. Brass, Yellow, 268
47. Uranium 8% Mo
48. Brass, Naval, 464
49. Yellow Brass
50. Muntz Metal 280
51. Brass (plated)
52. Nickel-silver (18% Ni)
53. Stainless steel 316L (active)
54. Bronze 220
55. Copper 110
56. Red Brass
57. Stainless steel 347 (active)
58. Molybdenum, Commercial pure
59. Copper-nickel 715
60. Admiralty brass
61. Stainless steel 202 (active)
62. Bronze, Phosphor 534 (B-1)
63. Monel 400
64. Stainless steel 201 (active)
65. Carpenter 20 (active)
66. Stainless steel 321 (active)
67. Stainless steel 316 (active)
68. Stainless steel 309 (active)
69. Stainless steel 17-7PH (passive)
70. Silicone Bronze 655
71. Stainless steel 304 (passive)
72. Stainless steel 301 (passive)
73. Stainless steel 321 (passive)
74. Stainless steel 201 (passive)
75. Stainless steel 286 (passive)
76. Stainless steel 316L (passive)
77. AM355 (active)
78. Stainless steel 202 (passive)
79. Carpenter 20 (passive)
80. AM355 (passive)
81. A286 (passive)
82. Titanium 5A1, 2.5 Sn
83. Titanium 13V, 11Cr, 3Al (annealed)
84. Titanium 6Al, 4V (solution treated and aged)
85. Titanium 6Al, 4V (anneal)
86. Titanium 8Mn
87. Titanium 13V, 11Cr 3Al (solution heat treated and aged)
88. Titanium 75A
89. AM350 (passive)
90. Silver
91. Gold
92. Graphite
Cathodic (More noble)

As mentioned in one of the posts above, the anode manufacturer would be the best source of advice.